Spent some time test riding a newly built size 52 X68 today. I brought my genuine S-Works SL8 (also size 52) along and did a fair few bike swaps to see if I could feel the difference.
Sadly I couldn't make an accurate comparison as the spec of both bikes are way different. I'm running SRAM Red E1 and he's running Wheeltop so the difference in hood/lever feel alone threw me off quite a lot (SRAM E1 levers just feel too good and being able to comfortably get all 4 fingers under the hoods makes a world of difference when sprinting out of the saddle IMHO).
We also had issues with the front derailleur cage hitting the crank arm due to flex when sprinting out of the saddle (sadly I scratched up his front mech!), but he managed to sort that out by tuning the Wheeltop during our ride.
Got to say, it's a fast bike. He did say multiple times that my bike felt like it rolled faster, but again, that could just be down to spec, specifically tyres as I'm running GP5000 TT TR's and he was running S TR's. That said he was running lighter ZEN Carbon Bike 50/50 deep wheels and I'm running CRW's 40/45's. Again, so much difference in spec, but no doubt about it, the X68 is a fast bike and it rides insanely good for the price, especially when you compare it to how much a genuine S-Works SL8 frameset costs.